The primary objective of this work was to describe biological assemblages associated with deep coral reef systems at Scott Reef in WA. A significant proportion of South Scott Reef and the adjacent lagoon lies in waters between 30 m to 70 m deep that support a range of habitats similar to many of the submerged shoal systems strung along the edge of the continental shelf in the Timor Sea. The South Scott Reef lagoon covers 300 km2 and is the largest area of this type observed on a single reef system in the NW region.
Understanding the nature and dynamics of these deeper water areas will not only better describe the true extent of Australia’s tropical reef resources, but will contribute to a broader understanding of the overall resilience of coral reefs in the NW region.
Scientific diving effort supporting a number of long term monitoring sites at Scott Reef is strongly biased towards depths of 20 m or less, with very few investigations on coral reefs venturing beyond 30 m. Remote sampling approaches are required to explore areas such as the deeper lagoon at Scott Reef. During the last decade a few surveys using simple towed video and small ROVs have begun to be used to survey the deeper South Scott Reef lagoon. The initial habitat maps derived from these surveys suffer from the coarse interpolation used to join a limited number of survey points. The quality of the video used has also severely restricted the taxonomic resolution possible, precluding accurate assessment of species distributions and has provided limited information for monitoring purposes. In order to produce an accurate, high resolution habitat map of the deeper reef waters and to establish viable deep water monitoring sites, high resolution acoustic mapping using digital mulitbeam form Geosciences Australia was completed in parallel with collecting georeferenced seabed images using the AUV Sirius operated by the IMOS AUV Facility and the existing AIMS towed video with high resolution stills systems. AUV deployments consisted of 19 dives over 12 days of operation onboard the R/V Solander using a mix of survey designs and illustrated the vehicle's reliability and versatility as a complementary habitat characterisation tool:
• Long (4 km to 8 km) transects along seafloor gradients designed to document coral reef communities beyond diving depths in depths from 30m to 110m
• Large scale (km2), sparse grids to determine spatial variability in habitat structure.
• Small-scale (2500-4000 m2), repeated contiguous coverage mapping for the establishment of potential long term monitoring site
On several occasions the vehicle operated beyond tracking range of the supporting vessel for extended periods facilitating the execution of other scientific objectives, particularly swath bathymetric mapping of the Scott Reef lagoon.